1. Field of the Invention
The present invention relates to a process for preparing a heat sensitive semiconductor switch which has high reproducibility to give a suitable switching temperature for switching from the OFF state to the ON state.
2. Description of The Prior Art
The semiconductor switch of the present invention has at least three PN junctions and has two stable states consisting of an OFF state and an ON state in the voltage-current characteristics between main electrodes which is usually called as a thyristor.
In the conventional thyristors, a rated maximum junction temperature is chosen to allow the use of thyristors only in a temperature range such that an OFF voltage is not decreased by increasing the junction temperature to prevent a turn on by a thermal change. The temperature for eliminating the OFF voltage by elevating the temperature is significantly higher than the rated maxmimum junction temperature. There is no conventional thyristor which switches from the OFF state to the ON state by a thermal change at relatively low temperature such as room temperature to 100.degree. C.
In order to obtain a semiconductor switch for switching from the OFF state to the ON state at relatively low temperature, it is necessary to increase a leakage current at the PN junction of the thyristor which is reversely biased in OFF state.
As the manner for increasing a leakage current, a region having many recombination centers is formed in a space charge layer of the reverse-biased PN junction. This is disclosed in Japanese Unexamined Patent Publication No. 146283/1975.
However, it has not been known to prepare a thyristor wherein the leakage current of the reverse-biase PN junction in OFF state is increased in high degree under excellent reproducibility.
It has been sought to attain such process in a practical operation.